Biogeographic and biostratigraphic implications of the - Australian ...

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14 Records of the Australian Museum (2009) Vol. 61 Fig. 7. Paroistodus parallelus (Pander, 1856). All from sample WCB705/133. A–D, M element; (A), CPC39842, anterior view (IY117-002); B,C, CPC39843, (B), anterior view (IY117-005); (C), basal view (IY117-006); (D), CPC39844, posterior view (IY117-008). E–G, Sa element; E,F, CPC39845, (E), lateral view (IY117-010), (F), basal view (IY117-011); (G), CPC39846, lateral view (IY117-009). H–J, Sb element; (H), CPC39847, outer lateral view (IY117-017); I,J, CPC39848, (I), inner lateral view (IY117-016), (J), basal view (IY117-018). K–M, Sc element; K,L, CPC39849, (K), basal view (IY117-014), (L), inner lateral view (IY117-013); (M), CPC39850, outer lateral view (IY117-012). N,O, Sd element; (N), CPC39851, inner-basal view (IY117-025); (O), CPC39852, outer lateral view (IY117-029). (P), Pb element; CPC39853, outer lateral view (IY132-020). Q–S, ?Pa element, (Q), CPC39854, basal view (IY117-036), (R), CPC39855, outer lateral view (IY117-030); (S), CPC39856, inner lateral view (IY117-034). Scale bars 100 µm.
Material. 457 specimens from three samples (Table 1). Remarks. The species as revised by Löfgren (1997) possesses a septimembrate apparatus (including makellate M and drepanodiform or paroistodiform S and P elements), which can be distinguished from the other species of Paroistodus by having prominent lateral costae on the sides of its constituent elements. Zhen et al. (in press b) preferred to describe the S and P elements as paroistodiform in the Paroistodus species which show a sharp anterior costa extending basally into the basal cavity and forming a ridgelike structure (Zhen et al., 2007b, p. 137) at the anterior end of the basal cavity. However this character is not shown in the material of the two Paroistodus species (similar to Paroistodus sp. recently documented from the Honghuayuan Formation in South China) reported herein from the Emanuel Formation, although the anterior part of base often exhibits a zone of recessive basal margin (Figs 7A–C, 8H). Paroistodus parallelus occurs abundantly in the Emanuel Formation, where it is found in association with P. proteus although the latter is rare (Table 1). Paroistodus proteus (Lindström, 1955) emend. Löfgren, 1997 Fig. 8A–K Drepanodus proteus Lindström, 1955: 566, pl. 3, figs 18–21, text-fig. 2a–f, j. Paroistodus proteus (Lindström).—Löfgren, 1997: 922–923, text-figs 3H–N, 4L–AB (cum syn.); Zhen et al., 2007b: 136, 137, pl. 5, figs 1–11 (cum syn.). Material. 30 specimens from three samples (Table 1). Remarks. Paroistodus parallelus is relatively rare in the Emanuel samples, and can be easily differentiated from associated P. parallelus mainly by lacking a prominent costa on the lateral faces. Paroistodus proteus was revised by Löfgren (1997) as having a septimembrate apparatus. After a review of previously reported occurrences of this species in the Honghuayuan Formation and other coeval stratigraphic units in South China and comparison with Baltic material of P. proteus, Zhen et al. (2007b) concluded that Paroistodus is represented in the Honghuayuan Formation by a rare form that they identified as Paroistodus sp. It differs from P. proteus in having a smooth lateral face without a carina and having a more open basal cavity which lacks the distinctive so-called paroistodiform character. The material from the Emanuel Formation is transitional between typical P. proteus from the late Tremadocian to Floian of Balto-Scandia and Paroistodus sp. from the Honghuayuan Formation of South China. It is comparable with P. proteus in having a prominent carina (Fig. 8A–E) or even a weak costa (Fig. 8J) on the lateral faces, but similar to Paroistodus sp. from the Honghuayuan Formation in lack of the paroistodiform feature. As mentioned above, absence of the paroistodiform character in species of Paroistodus co-occurring in the Emanuel Formation may indicate that this feature is caused by ecological adaption rather than as a phylogenetically Zhen & Nicoll: Canning Basin Serratognathus bilobatus Fauna 15 significant trait for Paroistodus. Interestingly, P. proteus from the Emanuel Formation of Western Australia and from the Latorp Limestone and Tøyen Shale of Sweden and Paroistodus sp. from the Honghuayuan Formation of South China come from three contrasting ecological/sedimentological settings; they may represent three populations or subspecies of P. proteus. The typical latest Tremadocian and early Floian P. proteus-bearing successions in Sweden (e.g., Diabasbrottet area) were deposited in the outer shelf settings of the Cold Domain (Bergström et al., 2004), and the mid-upper part of the Emanuel Formation might be largely deposited in deep subtidal settings, while the Honghuayuan Formation with Paroistodus sp. apparently represents typical shallow subtidal environments. Therefore, in consideration of the relationship between their morphological variation and their ecological/geographical distributions, the material from the Emanuel Formation is considered as conspecific with type material of P. proteus, and Paroistodus sp. from the Honghuayuan Formation (Zhen et al., 2007b) might be better treated as a separate subspecies of P. proteus. Prioniodus Pander, 1856 Type species. Prioniodus elegans Pander, 1856. Prioniodus adami Stouge & Bagnoli, 1988 Fig. 6G–L Prioniodus sp. nov. C McTavish, 1973: 47, pl. 3, figs 4–6, ?11, 16, text-fig. 6f, g, i, ?j, k. Prioniodus adami Stouge & Bagnoli, 1988: 132, 133, pl. 11, figs 5–13 (cum syn.); ?Albanesi et al., 1998: 155, pl. 10, figs 1–3; Johnston & Barnes, 2000: 36, pl. 16, figs 9, 10, 13–16, 19; Pyle & Barnes, 2002: 110, pl. 26, figs 19–21. Material. Four specimens from two samples (Table 1). Remarks. Based on a large collection from Bed 9 of the Cow Head Group of western Newfoundland, Stouge & Bagnoli (1988) established P. adami as having a septimembrate apparatus (pastinate Pa, and Pb, ramiform S and geniculate M elements), and also included in it the material from the Emanuel Formation that McTavish (1973), ascribed to Prioniodus sp. C except for the oistodiform element (his pl. 3, fig. 11, text-fig. 6j) which bears a short, adenticulate inner lateral process. Prioniodus adami is characterized by bearing small, closely-spaced denticles on the long posterior process of the S and P elements, as well as on the anterior and outer lateral processes of the P elements and the inner lateral process of the M element. The Pa element (Fig. 6G, H) from the Emanuel Formation is identical with those illustrated by McTavish (1973, pl. 3, figs 5, ?16), but exhibits less closely spaced denticles on the processes in comparison with the holotype (Stouge & Bagnoli, 1988, pl. 11, fig. 8). The M element from the Cow Head Group shows a long adenticulate outer lateral process and a long, denticulate inner lateral process with small, closely-spaced denticles, similar to those on the processes of the P and S elements, but no M element has been recovered from the samples of this study.
Page 1 and 2: © The Authors, 2009. Journal compi
Page 3 and 4: Zhen & Nicoll: Canning Basin Serrat
Page 7 and 8: late Floian to Dapingian age. An et
Page 11 and 12: Repetski (1982) were actually speci
Page 13: Drepanoistodus Lindström, 1971 Typ
Page 17 and 18: Scolopodus Pander, 1856 Type specie
Page 27 and 28: have a broad convex outer face and
Page 29 and 30: Löfgren, A., & T.J. Tolmacheva, 20

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